The choline acetyltransferase (ChAT) activity was measured in numerous discrete brain nuclei of 4-, 8-, and 12-wk old spontaneously hypertensive rats (SHR) and their age matched Wistar Kyoto control rats (WKY). The acetylcholine (ACh) concentration was also measured in hindbrain nuclei of 12-wk old SHR and WKY. Changes in ChAT activity of several nuclei were observed in SHR of all 3 age groups. The greatest alteration (79 percent increase) was found in the ChAT activity of the locus coeruleus of 12-wk old SHR. A 31 percent increase was found in the ChAT activity of the locus coeruleus of 12-wk old SHR. A 31 percent increase in ACh was also detected. No differences were found in this nucleus in 4-wk SHR. Other nuclei known to be involved in blood pressure control which showed differences in ChAT activity in SHR compared to WKY were the paraventricular nucleus, dorsomedial nucleus of the hypothalamus, posterior hypothalamus and the nucleus reticularis gigantocellularis. A significant increase was also found in the anterior ventral thalamus in 4- and 8-wk SHR.